Significant progress has been made in understanding
some of the basic mechanisms of force production and flow manipulation
in oscillating foils for underwater use. Biomimetic observations,
however, show that there is a lot more to be learned, since
many of the functions and details of fish fins remain unexplored.
This review focuses primarily on experimental studies on some
of the, at least partially understood, mechanisms, which include 1)
the formation of streets of vortices around and behind two- and
three-dimensional propulsive oscillating foils; 2) the formation of
vortical structures around and behind two- and three-dimensional
foils used for maneuvering, hovering, or fast-starting; 3) the formation
of leading-edge vortices in flapping foils, under steady flapping
or transient conditions; 4) the interaction of foils with oncoming,
externally generated vorticity; multiple foils, or foils operating
near a body or wall.